Respiratory Changes in Pregnancy

Pregnancy changes breathing through two linked mechanisms. Progesterone makes the respiratory centre more responsive to carbon dioxide, so ventilation rises. At the same time, the enlarging uterus elevates the diaphragm and reduces the amount of air left in the lungs after a normal exhalation. This combination explains why a pregnant patient may feel short of breath while maintaining normal oxygenation. It also leaves less respiratory reserve, so new hypoxaemia, marked tachypnoea, or increased work of breathing should not be dismissed as a normal pregnancy symptom.